From owner-freebsd-stable Sat Sep 27 06:15:27 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.7/8.8.7) id GAA22725 for stable-outgoing; Sat, 27 Sep 1997 06:15:27 -0700 (PDT) Received: from phoenix.its.rpi.edu (phoenix.its.rpi.edu [128.113.161.45]) by hub.freebsd.org (8.8.7/8.8.7) with ESMTP id GAA22720; Sat, 27 Sep 1997 06:15:20 -0700 (PDT) Received: from localhost (dec@localhost) by phoenix.its.rpi.edu (8.8.7/8.8.7) with SMTP id JAA25094; Sat, 27 Sep 1997 09:16:17 -0400 (EDT) Date: Sat, 27 Sep 1997 09:16:17 -0400 (EDT) From: "David E. Cross" To: sthaug@nethelp.no cc: tlambert@primenet.com, hackers@FreeBSD.ORG, stable@FreeBSD.ORG Subject: Re: 'fxp' driver/hardware lossage (was Re: Alexander B. Povol's mail) In-Reply-To: <17057.875363985@verdi.nethelp.no> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-stable@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk On Sat, 27 Sep 1997 sthaug@nethelp.no wrote: > > > That's only true of coaxial media. Over twisted pair, if you see > > > data start arriving on the receive pair while your transmitting then > > > you have to assume that the data is being sent by another station > > > and you've got a collision situation. > > > > Isn't this the hub's responsibility to distinguish and prevent? > > Nope. A hub doesn't do anything with collisions - it just propagates > them bit by bit. The NICs sense the collision. > > Steinar Haug, Nethelp consulting, sthaug@nethelp.no Technically this is not even a colission situation. Many new NICs and Hubs (both must support it to work) support full-duplex 10BaseT, allowing 20MBits/sec. I am not sure what happens when it gets into the hub and needs to be propogated to other ports though *shrug*. Anyway... multiple packets being transmitted at the same time is detected by the NIC, and the NIC then sends a jamming signal which stops all transmissions on the network for a random time (each card that was transmitting durring this time sets a ranom timer for how long to wait, and they all try to re-transmit, using exponential backoff if there are additional collisions). This jamming signal is the actual 'collision', and is what shows up as a colision light on hubs/external transcievers. Excellent and page-turning reading that 802.* ;) -- David Cross